To avoid cluttering my sky with bits of engine and fuel tank, I had the thought to strap some solid fuel boosters to stages pointed retrograde and activate them during staging in order to deorbit them. However, on the couple rockets I've tried this end up being damaged by their thrust and/or the brief shock when decoupling.

Is there a way to separate the stage then take control of it later to chuck it back into oblivion? Alternatively, can I have it just fire after a set time?

An action group delay timer is a common request, I haven't seen any mods with this functionality though
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authenticgeekMar 1 '13 at 21:22

If you really wanted to get fancy, you could build a spacecraft with some kind of claw, or the buran manipulator. Then, you can just fly to the debris and set them on a deadly orbit. However, this takes lots of time and skill...
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WijagelsApr 27 '13 at 15:51

@Wijagels ...and fuel, and can end up creating more junk just from the spent stages it takes to get the retrieval craft up there.
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IsziJul 25 '14 at 18:15

With the 0.24 update, de-orbiting spent stages - and landing them safely - is even more important now. See my related questions here and on Space.SE.
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IsziJul 25 '14 at 18:17

5 Answers
5

KSP does not allow remote control of unattached pieces. Anything not attached to your main cockpit automatically becomes directly uncontrollable as soon as it detaches.

That said, there are a few options available, if you're looking to de-orbit spent stages.

Create a dedicated deorbit vehicle that catches your debris, and burns retro to shed some speed. That's rather difficult, as everything needs to be intercepted individually.

Attach a probe cockpit (or MechJeb component) to the stage. This will allow you to switch your focus to it. I'd recommend ensuring your primary stage is in a stable orbit before doing so, as fully deorbiting something will take quite some time.

The last option is to turn off all debris entirely, as detailed in my answer here. That's the easy way out, but without specific tools to deorbit junk, it's rather involved to manually clean it up.

Any way you look at it, currently KSP doesn't allow control of parts that are not directly connected to your current focus.

Yes there is, if you have a component capable of issuing commands, and it is properly manned/powered. This typically means attaching probe bodies to each stage that you will want to control later.

I find this sub-optimal at best though. Performing a post separation deorbit typically means you need to save some fuel in order to do those burns. And since probe bodies don't have a lot of torque, you're going to have to make sure that you have sufficient RCS fuel and thrusters. There is one advantage here, in that RCS is typically enough by itself to deorbit something. However, this all adds weight to your rocket, weight that's better spent as saved fuel in sending your payload where you want it to go. For typical real life missions, hoisting an extra pound of payload to orbit could mean burning an extra five ten pounds of fuel.* That can get very expensive, very fast.

In my opinion, you're better off setting up stuff such that it falls back to the ground without your intervention, or setting up trajectories that will cause spent stages to impact the Mun (or other celestial body).

* This page lists some mass fractions required to achieve SST-LEO, as well as typical mass fractions for existing space vehicles. In an ideal world, a 5:1 fuel to payload ratio is theoretically possible, but that ignores the realities of atmospheric drag, incomplete combustion, and a number of other factors. The ratio for Soyuz is almost exactly 10:1.

No, you must have a command pod on a section in order to control modules on it. I've read of people having luck with making a rocket with landing legs on the front, and using it to push rocket parts into a decaying orbits. I haven't tried this, but I suspect you could stick a probe module on a stage, and use that to take control and deorbit it.

If this mod can solve the problem posed, can you add instructions on how to use these parts to do so? Just pointing to a mod by itself isn't very helpful.
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FrankFeb 18 '14 at 22:09

it should have a video on the thread that explains it, while i haven't used it yet because i have too many mods installed already and haven't got around to trying them out on a different game file it looked like it might solve this guy's problem. there's timers that can activated on a stage then activate other stages on their respective parts. once again i haven't played around with them yet, but i will today for the sake of this post)
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TheAmazing_OMEGAMar 6 '14 at 13:59

put sepratrons on your stages, turned 180 degrees, and simply included firing them in the stage that triggers the pertinent decoupler. with the exception of circularization stages this does a pretty fair job. might even work on those if you added enough of them...